The present invention is in the field of flue construction and is particularly directed to a flue construction which lowers outward heat flow from the lower portions of a flue in which the highest temperature combustion gases occur so as to reduce the likelihood of fire damage to the building; however, the inventive flue addition maintains higher temperatures in the upper portion of the flue to reduce the build up of creosote so as to reduce the likelihood of fire in the flue. It is a well known fact that flue gases are at their hotest temperature in the lower portion of flue and progressively cool as they flow upward toward the top of the flue so that in some instances there is a tendency for creosote and other products of combustion which are in a gaseous condition at the higher temperatures in the lower flue portions to condense as they engage the cooler upper walls of the flue defining member. If the lower portions of the flue are too hot, a fire hazard in the surrounding building structure is created; however, if the upper flue wall portions are too cool, a creosote hazard is created. While the creosote hazard can be reduced by having a higher temperature in the lower flue portions which results in a higher temperature in the upper flue portions, such an approach is unsatisfactory due to excessive heat loss and additional fire hazard resulting from the higher temperature in the lower flue portions.
Various constructions have been proposed by the prior art for dealing with the aforementioned problems. For example, U.S. Pat. Nos. 313,441; 843,797; 915,123; 1,457,454; 1,484,828; 1,566,233; 2,362,833; 2,634,720; 3,160,087; 2,687,127; 3,538,656; 3,531,845; 3,464,174; 2,916,983; 3,149,437 and 2,275,902 have disclosed various flue constructions employing air chambers or the like surrounding or adjacent the flue portion through which the hot combustion products flow. However, the devices of the prior art have not met with general acceptance as a consequence of several problems including high cost, functional defects, complexity and lack of versatility for use in different types of flue installation.
Therefore, it is the primary object of the present invention to provide a new and improved flue construction.
A further object of the present invention is the provision of a new and improved flue construction having substantially reduced fire hazard as compared to prior known constructions.